Can Opec defend an oil price of $100 a barrel? Yesterday the cartel, after its meeting in Vienna, seemed to signal that it wants to try. A cut in production of 500,000 barrels a day is tiny (about 0.6% of global production) but the tone of the communique was hawkish - it described the oil market as over-supplied. That sounded like a threat to reduce production further, through the formal mechanism of quotas, if prices continue to fall.

Yet the price of a barrel of Brent barely budged; it was back below $100 by the afternoon. The market clearly doubts Opec's ability to put a floor under prices after the fall from July's peak of $147. Consumption in the US fell sharply over the summer; autumn is traditionally the slow season for oil; and colder economic breezes are reaching Asia, source of the growth in demand for oil. So maybe Opec's stance was weaker than it appeared - after all, the heavy gun of quota cuts wasn't rolled out.

Predicting the oil market is a mug's game. A year ago, the idea that prices might soon hit $147 a barrel seemed silly. It seems equally likely that prices could overshoot on the way down - especially as Opec has advertised its concern that global recession will destroy demand. That's not a position of strength.

Lehman bravado

It's a miracle. Lehman Brothers doesn't need new capital or new investors.

The message was not the one Wall Street was expecting to hear. Nor was it simple. It seems that the sale of a 55% stake in the investment management business, plus a spin-off of the poisonous commercial property assets into a separate vehicle, can allow a "core" Lehman to emerge. There was an odd-looking goodwill write-back in there to help the calculations but you get the picture: Lehman thinks it can muddle through in a slimmed-down version.

Chief executive Dick Fuld claimed his staff (the ones who are left) are "holding wonderfully" and that clients are supportive. He has to say that, but the harsh reality is that a wounded investment bank is a vulnerable creature on Wall Street. Rivals pick off top talent and a shrinking bank finds itself with less financial firepower. A takeover looks the most likely outcome.

Hedged in

Investors in RAB Capital's Special Situations hedge fund thought life was bad last week, when they were told that the value of their investment was down 37.5% this year. Yesterday, after adding up the latest numbers and reviewing the unlisted portfolio, RAB told them that the fall is now 48%.

Cue a rush for the exit, you might assume. But RAB wants to bolt the door. It is asking investors, who include the steel billionaire Lakshmi Mittal, to agree to lock up their money for three years. In return, it will reduce its fees.

The lock-in proposal may well succeed. Philip Richards, the fund's manager, is best known for his bad bet on Northern Rock, but his fund is really stuffed with small mining and resource stocks. Selling these into a falling commodity market risks instantly turning a 48% loss into something much worse. Thus the invitation to ride the downturn and await the upturn. The fund's wealthy backers (minimum investment: $50,000) may well look kindly on Richards' long-term record (a 17-fold return since 2003, even after this year's shocker) and let him carry on.

But RAB's woes also reveal the wider ones of the battalion of hedge funds operating in the commodity field. Investors, having enjoyed the boom, want out. US manager Ospraie has pulled the plug of one of its big commodity funds. The providers of hedge funds' debt, the investment banks, don't want another black hole to appear and are imposing tougher terms. We're seeing a spiral of selling, and it shows no sign yet of slowing. Expect more casualties.